Essential Science: Planets close to dim stars may support life

The question of whether life exists on other planets in the depths of our galaxy continues to intrigue people. If we are to find out that we are alone in the universe then examining planets orbiting dim red stars might provide the answer.

One group of astrophysicists think life might have well exist on planets orbiting dim red stars. However, they caution, if such exoplanets orbiting the types of stars classified as M dwarfs do host life, then this 'life' is very probably quote different from what we're used to on Earth.

M dwarfs are one of two types of red dwarfs (the other being class K stars). These are small and relatively cool stars; they are also very-low-mass stars. Red dwarfs are by far the most common type of star in the Milky Way (perhaps making up 70 percent of the stars in our galaxy). The closest star to the sun, Proxima Centauri, is a red dwarf (which lies in the southern constellation Centaurus). Many red dwarfs are orbited by exoplanets.

Artist's depiction of Jupiter-like exoplanet in a solar system far far away.

Latitude0116 / Wikimedia Commons

An exoplanet (or what is sometimes called an extrasolar planet) is a term applied to a planet outside of our solar system that orbits a star. Astronomers, and organizations like NASA, have been cataloging exoplanets (NASA maintains an exoplanet archive). As of 1 June 2017, there have been 3,610 exoplanets, in 2,704 planetary systems and 610 multiple planetary systems.

Chance of other life in our galaxy?

The probability of a civilization developing on a potentially habitable alien planet would have to be less than one in 10 billion trillion — or one part in 10 to the 22nd power — for humanity to be the first technologically advanced species the cosmos has ever known (at least according to one classic study).

One reason why there's often considerable excitement about the discovery of some exoplanets is connected with the search for extraterrestrial life. Particular interest is paid to planets that orbit in a star's habitable zone, since it is possible for liquid water, a prerequisite for life on Earth, to exist on the surface of these worlds. In addition, any study of planetary habitability also considers a wide range of other factors in determining the suitability of a planet for hosting life.

This graphic contains an image and illustration of a nearby star, named CoRoT-2a, which has a planet in close orbit around it.

NASA

As an example, a 'mere' 39 light-years away from Earth, seven planets, all roughly the size of Earth, whirl around a dim red star dubbed TRAPPIST-1. The planetary system was detected by the TRansiting Planets and PlanetIsmals Small Telescope (TRAPPIST) and NASA's Spitzer Space Telescope.

One reason for focusing on red dwarfs and their planets, Science News reports, is because so many of them tick the box for being potentially life supporting. Of the roughly 200 planets that have been spotted around M dwarfs, dozens are in within the theoretical 'habitable zone'.

This global view of Jupiter's moon, Io, was obtained during the tenth orbit of Jupiter by NASA's Galileo spacecraft. Io, which is slightly larger than Earth's Moon, is the most volcanically active body in the solar system.

NASA/JPL/University of Arizona

Going back to the closest star to our own, Proxima Centauri, there is considerable interest in a planet called Proxima b which orbits the star. This is because the temperature is just right for liquid water to flow on its surface. In addition, starlight appears to filter through the planet’s atmosphere suggesting the presence of atmospheric gases. These factors have been highlighted in a recent issue of the publication Nature ("A terrestrial planet candidate in a temperate orbit around Proxima Centauri").

The lead researcher Guillem Anglada-Escudé (of Queen Mary University of London) suggests another favorable factor is the planet being no lighter than 1.3 Earths. NASA’s James Webb Space Telescope, scheduled to launch in late 2018, should be able to characterize its atmosphere of Proxima b and reveal more of its secrets.

While further revelations may appear next year, it remains likely that we'll require further advancements in technology before conclusive evidence can be accumulated to indicate if such planets orbiting red dwarfs can support life. In the meantime, the class M stars remain the key targets for the quest for extraterrestrial life.

NASA's Spitzer Space Telescope has found that the hottest part of a distant planet, named upsilon Andromedae b, is not under the glare of its host star as might be expected.

Image: NASA/JPL-Caltech

In related planetary news, new findings from the University of Münster suggest Jupiter was one of the earliest objects to form in our solar system. Based on new measurements of meteorite ages, the German researchers suggest the giant planet’s core will most probably have formed within the solar system’s first million years.

Essential Science

This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week we looked at how the microorganisms found in hospitals alter over time and the explored the routes by which patients might become infected. The week before we delved into a new technique that looks at reducing skin aging, by applying methylene blue.